1. Field of the Invention
This invention relates to measuring and testing of corrosion processes, and it relates more particularly to a probe system for measuring molecular hydrogen gas created by the corrosion of ferrous metals.
2. Description of the Prior Art
It is often desirable to determine the rates at which ferrous metals corrode within a corrodant, such as a corrosive aqueous liquid. For example, corrosion inhibitors are added to aqueous liquids to reduce the corrosion of exposed metals. Instruments are used to measure the rates at which these metals corrode so that the effectiveness of inhibitor addition can be determined. One measurement of the rate of corrosion upon ferrous metals involves the determination of the amount of molecular hydrogen created by the corrosion reaction of a ferrous metal exposed to a corrodant. For example, a steel sidewall of a pipeline carrying a corrodant, such as hydrogen sulfide in water, has a corrosion reaction creating atomic hydrogen which diffuses through the sidewall and released exteriorly as molecular hydrogen gas. Escape of the molecular hydrogen gas from the sidewall permits the corrosion reaction to continue. However, the molecular hydrogen gas escaping the sidewall can oftentimes build up to a sufficient pressure causing physical injury such as blistering and rupturing of the sidewall's exterior surface.
Various measurements systems have been proposed for the measurement of the molecular hydrogen gas produced by the corrosion reaction. For this purpose, a probe may be inserted through the sidewall of the pipeline and arranged to measure the molecular hydrogen gas pressure buildup within the probe. For this purpose, the probe has a ferrous metal body in which there is formed a cavity. The corrosion reaction produced by the corrodant surrounding the probe causes molecular hydrogen gas to accumulate within the cavity. A pressure gauge mounted atop the probe indicates the actual pressure of the hydrogen gas accumulating within the cavity. For example, in very active corrodants, the pressure buildup of such a probe can reflect hydrogen gas accumulations within the cavity from an initial 15 psi to about 100 psi within a 24-hour period. The probe carries a manual venting valve so that the pressure can be released from the cavity when the pressure limits of the gauge are reached. Thus, this type of hydrogen measurement probe must be employed in a supervised manner wherein the operator can periodically record the readings of the probe and also vent hydrogen gas as necessary to prevent the destruction of the pressure gauge. This type of hydrogen measurement probe is simple and relatively inexpensive but has not found extensive utilization in the industry because of the requirement for relatively constant supervision.
Another type of hydrogen measurement probe avoids the supervision problem but employs a sophisticated gas ionization instrumentation principle. In this probe, the hydrogen gas is vented in a relatively continuous manner from the cavity within the probe body. The vented gas flows through an ionization chamber and detector sensor whose output is measured upon a scalar instrument indicating both total gas volume and rate of gas flow. This probe and readout instrumentation is relatively accurate, very expensive and dependable, but requires careful calibration and complicated installation. Also, this probe is relatively delicate for use unattended within oil fields, refineries and chemical plants.
The hydrogen probe system of the present invention is arranged to provide the simplicity of construction and operation of first mentioned probe with the utility and accuracy of the second mentioned hydrogen measurement probe but without its great expense and other accompanying problems.